|Red Hat Enterprise Linux 3: Using as, the Gnu Assembler|
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; is the line comment character.
$ can be used instead of a newline to separate statements. Therefore you may not use $ in symbol names on the H8/300.
You can use predefined symbols of the form rnh and rnl to refer to the H8/300 registers as sixteen 8-bit general-purpose registers. n is a digit from 0 to 7); for instance, both r0h and r7l are valid register names.
You can also use the eight predefined symbols rn to refer to the H8/300 registers as 16-bit registers (you must use this form for addressing).
On the H8/300H, you can also use the eight predefined symbols ern (er0 … er7) to refer to the 32-bit general purpose registers.
The two control registers are called pc (program counter; a 16-bit register, except on the H8/300H where it is 24 bits) and ccr (condition code register; an 8-bit register). r7 is used as the stack pointer, and can also be called sp.
as understands the following addressing modes for the H8/300:
Register indirect: 16-bit or 24-bit displacement d from register n. (24-bit displacements are only meaningful on the H8/300H.)
Register indirect with post-increment
Register indirect with pre-decrement
Absolute address aa. (The address size :24 only makes sense on the H8/300H.)
Immediate data xx. You may specify the :8, :16, or :32 for clarity, if you wish; but as neither requires this nor uses it--the data size required is taken from context.
Memory indirect. You may specify the :8 for clarity, if you wish; but as neither requires this nor uses it.